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Bottlehead Forum Welcome! Need support, you got it. Or share you ideas and experiences. |
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In Reply to: Re: Question Re: choice of tube for line level crossover filters posted by Ian L on November 29, 2005 at 16:02:23:
Most use cathode followers because the Sallen & Key circuits commonly used calls for a unity gain active circuit. Actually, there are several popular circuits that call for a fixed gain, usually in the range of 1 to 3 - which is easy with opamps but kind of clumsy with tubes.I don't see noise as an issue at line level, so I don't know - and don't really care - what some marketing department is talking about... :^)
For a cathode follower, gm determines the output impedance; a lower rp for a given gm will let you run more current so it can drive a lower load impedance comfortably. So yes, a tube with more "beef" would be preferable. That's what we did to the studio's Marchand. Watch out for too much transconductance though - cathode followers are (the simplest kind of) feedback amplifiers, and they can go unstable at very high frequencies if the layout, lead dress, and phase of the moon are against you.
For profit or not, I would use a cathode follower. That's what we have been doing with the Climax development. Naturally I would load it with a C4S and shunt reg the power supply. Once we get the FP-III C4S/shunt reg kit going, I'll probably make up a Climax crossover on a FP chassis - it's kind of a natural platform for a modest 2-way.
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Follow Ups
- Re: Question Re: choice of tube for line level crossover filters - Paul Joppa 17:07:29 11/29/05 (1)
- Thanks very much Paul - Ian L 23:52:43 12/01/05 (0)
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